1. Field of the Invention
The present invention relates to an optical device provided with a pedestal for mounting an optical element such as an optical isolator, and in particular, to an optical device which is appropriate for optical communication.
2. Description of the Background Art
In recent years, transmission of optical signals and optical energy using optical fibers has been carried out actively, in fields such as optical communication and optical measurement, along with the development of optical technology. In such systems, it is necessary to optically couple light sources, photo receivers, wave filters and optical elements for sensing to optical fibers, and in addition, miniaturization of coupling parts is required.
An optical connector type part for a connection to an optical connector where a filter is installed in a ferrule has been proposed in, for example, Japanese Unexamined Patent Publication No. H5 (1993)-60934. Concretely speaking, a slit which crosses the through hole for the fiber of a ferrule is created, and an optical element, such as an optical filter, is placed within this slit. This structure, however, becomes complicated, because a number of coupling members are used in addition to the body of the ferrule, increasing the entire length. In addition, the creation of the slit causes a great insertion loss. In a single mode fiber, though the loss is comparatively small in the case where the slit width is approximately 200 μm or smaller, the loss of the slit portion exceeds 10 dB in the case where the slit width exceeds 400 μm, making it impossible to use as a conventional device. Accordingly, such an optical connector type part cannot be utilized for a large optical element of which the thickness exceeds 700 μm, like an optical isolator.
In addition, a method for simply connecting an optical isolator to a connector has been proposed in Japanese Unexamined Patent Publication No. H7 (1995)-84143. A polarization independent type optical isolator is used in a manner where the optical isolator is sandwiched by beam conversion elements from both ends for optical coupling, and these are fixed within a slotted sleeve. In this example, the problem of insertion loss has been solved by using beam conversion elements. Here, a core expansion fiber which is difficult to manufacture as beam conversion elements has been assumed. In addition, a birefringent single crystal is used for the polarization independent type isolator, leading to a problem where the system becomes complicated, in comparison with a polarization dependent type isolator.
Japanese Unexamined Patent Publication No. 2001-311851 shows a structure where a recess is created in a ferrule, to which an optical fiber body formed of a single mode fiber, a graded index fiber and a coreless fiber is fixed, and a polarization dependent type optical isolator is installed in this recess. In addition, Japanese Unexamined Patent Publication No. 2003-161838 discloses an installment of an annular protective member around this recess. These structures allow an appropriate optical coupling (optical connection) to an optical fiber to be implemented by means of compact configuration of parts.